Fuel economy of a vehicle may be displayed to an operator of the vehicle as a long term average and/or an instantaneous fuel economy reading. The instantaneous fuel economy reading provides real time fuel consumption data allowing the operator to adjust her/his driving style for improved fuel economy. However, the displayed instantaneous fuel economy readings may have large variations due to stored kinetic and potential energy, e.g., a zero at acceleration and an infinite value at deceleration, making such readings useless to the operator unless heavily filtered.
An example approach of adjusting mileage display for stored energy is shown by Sim in US 2011/0276260. Herein, an effective amount of consumed fuel is determined by measuring an actual amount of fuel consumed, and subtracting a fuel equivalent for each of stored energy and consumed energy from the actual amount of consumed fuel. A mileage based on the amount of effective fuel amount is then displayed to an operator of the vehicle.
However the inventors herein have identified potential issues with the above approach. As an example, the above approach utilizes extensive on-board computations and measurements that are stored in the memory of the vehicle prior to delivery from a factory. For example, the fuel equivalent for stored energy incorporates a conversion coefficient which is related to a dynamic energy storage efficiency and an electric energy storage energy efficiency. These efficiencies are measured on bench with energy being supplied by a generator separate from the vehicle, and are stored in the vehicle memory as a priori information. Further, an altitude change is measured via an inclinometer installed in the vehicle body which may be prone to an offset error based on the loading of the vehicle. The approach by Sim also involves multiple complicated and intensive computations including a vehicle mass calculation to determine stored kinetic and potential energy, a rotational angular velocity calculation to determine rotational speed, and a battery power calculation to determine stored electrical energy.
The inventors herein have identified an approach to at least partly address the above issues. In one example approach, a method for an engine in a vehicle is provided that utilizes a conversion factor for stored energy. The method comprises, when the vehicle undergoes a sufficient change in one or more of square of vehicle speed and vehicle altitude, estimating a conversion factor for fuel due to stored vehicle energy and adjusting a fuel economy reading by the estimated conversion factor. In this way, a simplified approach without excessive inputs may be used to compensate a fuel economy reading for stored energy.
For example, when a vehicle is traveling under steady state driving conditions, e.g. during cruising conditions, a fuel economy reading in miles per gallon (MPG) may be calculated. Steady state driving conditions may include conditions when changes in each of a square of vehicle speed and a vehicle altitude are below a respective threshold. During conditions when the vehicle experiences a sufficient increase in one or both of a square of vehicle speed and vehicle altitude, a conversion factor may be determined based on the fuel economy reading calculated at steady state driving conditions. Thus, the conversion factor may be determined when energy is being added to the vehicle system as one or both of kinetic energy and potential energy. The conversion factor may be based on an estimated fuel flow due to stored vehicle energy which is calculated by subtracting a fuel flow rate measured during steady state driving conditions from an existing fuel flow rate. As such, a difference between excess fuel flow during conditions when energy is being added to the system and steady state fuel flow may be used to determine the conversion factor for vehicle stored energy. The conversion factor may be directly proportional to fuel flow due to stored vehicle energy and inversely proportional to each of a change in square of vehicle speed and a change in vehicle altitude. The change in vehicle altitude may be measured by an inclinometer and corrected for offset error due to vehicle loading issues. The conversion factor may then be used to compensate a measured fuel economy reading for changes in stored energy.
In this way, a conversion factor can be learned based on fuel flow, a change in vehicle altitude, and a change in square of vehicle speed, every time specific conditions are met and may be stored in a controller's memory. Likewise, fuel economy readings during steady state driving conditions may be computed when certain conditions are met and stored in the controller's memory. The controller may be configured to use a rolling average of each of these readings when performing further calculations. The correction for fuel economy readings may be steadily improved by recurrently learning and adapting the conversion factor as the vehicle is being driven. Thus, laborious on-bench calculations of efficiency, a priori knowledge of fuel energy, and on board calculations of vehicle mass may be reduced by learning the conversion factor as described. Overall, a simpler methodology for compensating instantaneous fuel economy for stored energy is provided that may be used across vehicles which use different fuels, as engine efficiencies fluctuate, and as changes in vehicle mass are encountered.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.